I would read this thread here.
Silica and calmag
I used to do cal mag first, then base nutes, then pH up with silica. Then I read that thread. Now, if using silica, I would add it first, then base nutes, cal mag last.
Some expert growers find that silica affects flavor, so they cut it in week 5-6. Some cut cal mag too. There's a good thread on a different forum ("Silica" on thcfarmer). Here's a quote from it.
I usually taper down during flower just like cal-mag, cutting it completely on week 6 on a 9 week strain.